11 a atividade fitotóxica de parthenium contra trigo e canola

Planta Daninha, Viçosa-MG, v. 34, n. 1, p. 11-24, 2016

11Phytotoxic activity of parthenium against wheat and canola ...

1 Recebido para publicação em 4.9.2015 e aprovado em 5.10.2015.2 University of Agriculture, Faisalabad-Pakistan, <[email protected]> 3 Muhammad Nawaz Shareef University of Agriculture,Multan, Pakistan; 4 University of the Punjab, Quaid-e-Azam Campus, Lahore, Pakistan; 5 Huazhong Agricultural University, Wuhan,Hubei 430070, China <[email protected]>; 6 King Abdulaziz University, Jeddah, Saudi Arabia.

PHYTOTOXIC ACTIVITY OF PARTHENIUM AGAINST WHEAT AND CANOLADIFFER WITH PLANT PARTS AND BIOASSAYS TECHNIQUES1

A Atividade Fitotóxica de Parthenium contra Trigo e Canola Difere com Partes de Plantas eTécnicas de Bioensaios

KHALIQ, A.2, ASLAM, F.2, MATLOOB, A.2,3, JAVAID, A.4, TANVEER, A.2, HUSSAIN, S.5, andIHSAN, M.Z.6

ABSTRACT - Phytotoxic effects of invasive weed Parthenium hysterophorus were studied byusing whole plant, leaf and root aqueous extracts at 0, 2.5, 5.0, 7.5 and 10% (w/v)concentrations against germination and early seedling growth of wheat and canola. Studieswere carried out both in Petri plates with filter paper as substratum placed in controlledconditions and soil-filled plastic pots placed in open environments. Pronounced variationwas noted for phytotoxic activity of different plant parts of parthenium, aqueous extractconcentrations, test species, and bioassay techniques. Aqueous parthenium extracts eitherinhibited or delayed the germination and suppressed seedling growth of test species overcontrol. For both test species, all the germination attributes were suppressed to a greaterextent in Petri plates than in plastic pots. Leaf extracts were more suppressive to germinationof test species than whole plant and root extracts. Increasing extract concentration beyond2.5% caused significant reduction in seedling dry biomass of both test species. Aqueousparthenium extract diminished chlorophyll contents of wheat and canola by 32-63% and29-69%, respectively. Nevertheless, an increase of 9-172% and 22-60% in phenolic contentsof wheat and canola was recorded. Canola appeared to be more susceptible than wheat at allextract concentrations. Present study concluded that bioassays conducted under controlledcondition using filter paper as substratum may be misleading due to over estimation ofallelopathic response and variation in potential of receiver and donor species. Furthermore,it implies that threshold concentrations of allelochemicals for test species in Petri platesare rarely reached under field conditions.

Keywords: allelopathic inhibition, aqueous extracts, bioassay techniques, germination dynamics, parthenium,phenolics, seedling growth.

RESUMO - Foram estudados os efeitos fitotóxicos da planta daninha invasora Partheniumhysterophorus, por meio de extratos aquosos de plantas integrais, folhas e raízes em concentraçõesde 0, 2,5, 5,0, 7,5 e 10% (w/v), sobre a germinação e o crescimento inicial de plântulas de trigo ecanola. Foram realizados estudos tanto em placas de Petri com papel-filtro quanto em substratocolocado em condições controladas e vasos de plástico cheios de solo colocados em ambientesabertos. Variação pronunciada foi observada na atividade fitotóxica de diferentes partes da plantaParthenium, nas concentrações de extrato aquoso, na espécie de teste e nas técnicas de bioensaio.Extratos aquosos de Parthenium inibiram ou retardaram a germinação e o crescimento suprimido deplântulas das espécies de teste, em relação ao controle. Para ambas as espécies de teste, todos osatributos de germinação foram suprimidos em uma extensão maior em placas de Petri do que emvasos de plástico. Os extratos de folhas foram mais supressivos à germinação de espécies de testedo que as plantas integrais e os extratos de raízes. O aumento da concentração do extrato além de2,5% causou redução significativa na biomassa seca de plântulas nas duas espécies de teste. Oextrato aquoso de Parthenium diminuiu os teores de clorofila em trigo e canola em 32-63% e 29-69%,respectivamente. No entanto, aumentos de 9-172% e 22-60% em conteúdo fenólico de trigo e canola

Gisele Higa

Texto digitado

doi: 10.1590/S0100-83582016340100002

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foram registrados. A canola pareceu ser mais suscetível do que o trigo a todas as concentrações doextrato. Concluiu-se que bioensaios realizados sob condições controladas, utilizando papel-filtrocomo substrato, podem ser enganosos devido à sobrestimação da resposta alelopática e variação nopotencial das espécies receptoras e doadoras. Além disso, isso sugere que os limites de concentraçõesde aleloquímicos para as espécies de teste em placas de Petri raramente são atingidos em condiçõesde campo.

Palavras-chave: inibição alelopática, extratos aquosos, técnicas de bioensaios, dinâmica de germinação, parthenium,compostos fenólicos, crescimento de plântulas.

(Qasem & Foy, 2001; Khaliq et al., 2013b).Allelopathic interference by parthenium iswell documented and almost all plantparts, including pollen and trichomes, areknown to possess a number of water-solubleallelochemicals predominantly as phenolicacids and sesquiterpene lactones (Kohli et al.,2006; Aslam et al., 2014).

Bioassays are widely used to demonstrateallelopathy due to their usefulness as an earlyproof of allelopathic activity, low cost involved,easy execution and replication (Inderjit &Weston, 2000). Evaluating the influence ofallelopathic extract on the germination andseedling growth of test species has been themost widely used technique for such bioassays.However, contrary to bioassay studies, thesuppression achieved under field conditionsis often negligible (Duke et al., 2001), andresults vary under controlled and naturalconditions (Inderjit & Weston, 2000) merelybecause an array of factors interact eithersimultaneously or sequentially under fieldconditions. Bioassays conducted undercontrolled conditions using filter paper as asubstratum can be misleading due to anoverestimation of the allelopathic response andthe potential of the receiver and donor species.Inderjit & Weiner (2001) have asserted that,in order to achieve a better understanding ofthe subject matter, allelopathy should beconceptualized in terms of soil ecology. Withoutsoil, any growth bioassay can be misleadingwith a little or no ecological relevance (Foy,1999). Parthenium is getting increasingsignificance as a noxious invasive weed.Despite the availability of the volumetricliterature on the allelopathic potential of thisweed (Mersie & Singh, 1988; Swaminathanet al., 1990; Tefera, 2002; Rashid et al., 2008;Aslam et al., 2014) and foregoing research,results are difficult to be generalized and

INTRODUCTION

Parthenium (Parthenium hysterophorus)is an aggressive and troublesome weedwith a strong invasive potential (Javaid et al.,2011). Although native to tropical America(Picman & Picman, 1984), its infestationhas remarkably increased during the last20-30 years in both cropped and non-croppedareas in Pakistan (Marwat et al., 2008;Khaliq et al., 2015). It has been recognizedas a serious weed responsible for loss of cropproductivity, fodder scarcity, biodiversitydepletion and adverse effects on animaland human health (Tefera, 2002; Singhet al., 2005; Javaid & Riaz, 2012). The rapidexpansion and widespread distribution of thisweed is a challenging threat to the productivityand sustainability of agro-ecosystems. Thesuccess of this weed as an invader has beenattributed to rapid growth, high fecundity,greater acclimatization potential and, aboveall, interference by resource depletion andallelopathy (Marwat et al., 2008).

Allelopathy is a mechanism throughwhich weeds often affect the germinationdynamics and growth of field crops (Qasem &Foy, 2001) and promote weedy monoculturesby influencing species patterning in agro-ecosystems (Weston & Duke, 2003). Releaseof allelochemicals by living as well as dead weedtissues left in the soil after the completion oflife cycle has deleterious effects on the sameor subsequent plants (Batish et al., 2002;Khaliq et al., 2013a; Khaliq et al., 2015).Allelochemicals are reported to be present inalmost all plant parts, including stems, leaves,flowers, buds, pollen grains, seeds, fruits, rootsand rhizomes (Qasem & Foy, 2001). Differencesare also observed amongst species regardingtheir allelopathic potential and abilities toproduce toxins in various plant parts



implemented under field conditions as manyof these studies were conducted under controlconditions neglecting the components of thenatural setting.

The present work attempts to explore thephytotoxic potential of parthenium againstcrops of economic significance. The objectiveswere to ascertain (1) whether aqueousextracts of different parts of parthenium affectthe germination and growth of wheat andcanola, and to what extent under controlledconditions, (2) whether soil application of theseextracts under open environments producesthe same results in pot experiments, and(3) to rank the different plant parts for theirphytotoxic potential and test species in termsof susceptibility.

MATERIALS AND METHODS

Preparation of extract

Field grown plants of parthenium werecollected at flowering stage and respectivefractions (whole plant, leaves and roots) wereseparately dried in the shade. These werechopped into 2-3 cm pieces and oven dried at50 oC for 48 h. These were separately groundand passed through a 40 mesh screen. Groundpowder was soaked in distilled water at10 g 100 mL for 24 h at room temperature(25±2 oC). The filtrates of the respective plantfractions were obtained after passing themixture through a Whatman # 42 filter paper.These extracts were designated as 10% w/v

stock solutions. These were used either assuch or diluted with distilled water to preparelower concentrations of 2.5, 5.0 and 7.5%.

Biochemical attributes of aqueous extracts

The pH and electrical conductivity (EC) ofdifferent concentrations of the aqueousextracts of different parts of parthenium wereworked out using a digital pH and a conductivitymeter (HI-9811, Hannah, USA). The osmoticpotential was determined using the followingformula:

Osmotic potential (-Mpa) = EC (ds m-1) × -0.036

Total water-soluble phenolics in aqueousparthenium extracts were quantified as perSwain & Hillis (1959) using Folin-Ciocalteu’sreagent and expressed as ferullic acidequivalent as it has been reported to be a majorallelochemical in parthenium tissues (Singhet al., 2005). Measurements were taken byrepeating the whole procedures twice, andaverage values are given in Table 1.

Lab experiment: Influence of aqueousextracts of parthenium on germination ofwheat and canola in Petri plates

Aqueous extracts of whole plant, leavesand roots of parthenium at differentconcentrations viz., 0, 2.5, 5.0, 7.5 and 10.0%were evaluated for their effects on thegermination of wheat and canola. Fifteensurface sterilized seeds of test species wereevenly placed between two layers of Whatman

Parthenium plant fractions

Extract concentration

(%) pH EC (ds m-1)

Osmotic potential (-MPa)

Total soluble phenolics (µg ml-1)

2.5 6.8 1.43 0.05 74.21 5.0 6.7 2.63 0.09 220.53 7.5 6.6 3.69 0.13 312.11

Whole plant

10.0 6.6 4.69 0.17 510 2.5 7.8 1.55 0.06 503.68 5.0 7.5 3.07 0.11 817.37 7.5 7.5 4.43 0.16 1047.89 Leaf

10.0 7.1 5.63 0.20 1345.76 2.5 7.7 1.05 0.04 0.53 5.0 7.5 2.07 0.07 33.16 7.5 7.5 3.15 0.11 39.47 Root

10.0 7.2 4.06 0.15 125.79

Table 1 - Chemical properties of different concentrations of aqueous parthenium extracts

KHALIQ, A. et al.


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# 42 filter paper in sterilized Petri plates(9 cm diameter). Extract of the respectiveextract fraction (5 mL) and concentration wasadded to each Petri plate while the samevolume of distilled water was applied in thecontrol treatment. Half of the extract was usedfor moistening the filter paper receiving theseeds, while the remaining was applied to thecovering filter paper (Khaliq et al., 2013b).Germination counts were recorded on a dailybasis according to AOSA (1990) until a constantcount was achieved. Seeds were consideredto be germinated when radicle and hypocotyllength was over 2 mm. Time taken to 50%germination of seedling (T50) was calculatedaccording to the modified formula of Farooqet al. (2005) as below:

injn

)itj(tin2N

it50T−

−

−

+=

N is the final number of germinated seeds,and ni and nj are the cumulative numbers ofseeds germinated by adjacent counts at timesti and tj where ni < N/2 < nj. Mean germinationtime (MGT) was calculated according to Ellis& Robert (1981):

=

nDn

MGT

where n is the number of seeds, which weregerminated on day D, and D is the numberof days counted from the beginning ofgermination. Germination index (GI) wascalculated as described by AOSA (1983):

cout final of Daysseeds germinated of No.

count first of Daysseeds germinated of No.GI

+

−−−+=

Screen house experiment: Influence ofsoil-applied aqueous extracts ofparthenium on emergence, seedlinggrowth and biochemical attributes ofwheat and canola

Pot bioassays

Fifteen surface sterilized seeds of both testspecies were sown in separate themocol trays

measuring 18 x 14 cm filled with air dried andwell mixed field soil (750 g). Soil belongs to theLyallpur soil series (Aridisol-fine-silty, mixed,hyperthermic Ustalfic, Haplargid in the USDAclassification, and Haplic Yermosols in the FAOclassification). The pH of the saturated soilpaste and EC of the saturation extract were7.6 and 0.41 dS m-1, respectively. Aqueousextracts (10 mL) of different partheniumfractions (whole plant, leaves and roots) atdifferent concentrations (2.5, 5.0, 7.5 and 10%)were applied just after sowing the seeds. Thepots with distilled water application weremaintained as control. These pots were placedin a screen house under natural conditionswith 11/13 h light/dark period. Pots weresubsequently irrigated as and when requiredto keep the soil moist and to avoid water stress.

The emergence data were collected on adaily basis (AOSA, 1990) and were used tocompute different attributes of emergence astime to start emergence (TSE), time taken to50% emergence (E50), mean emergence time(MET), emergence index (EI) and finalemergence percentage (FEP) as described ina previous section. Two weeks after theemergence, seedlings were uprooted and rootand shoot length were determined with ameasuring tape. Seedling roots and shootsfrom each pot were oven dried separately at70 °C for 48 h and weighed thereafter. Totalseedling biomass was calculated as the sumof the biomass of root and shoot.

Biochemical analyses

Seedling fresh tissue (leaf) was used fordetermination of total soluble phenolics(Randhir & Shetty, 2005) that were expressedas gallic acid equivalents. Photosyntheticpigments (chlorophyll contents) wereextracted in ice cold acetone (80%) and readout at 663 and 645 nm wavelength in a UV-spectrophotometer (UV-4000, ORI, Germany).These are expressed as mg g-1 fresh leaf weight(Lichtenthaler, 1987). Determinations weremade as per treatment and replications.

Experimental design and statisticalanalyses

All the experiments were conducted usinga completely randomized design with four



replications and repeated once. Results of bothrepeats were similar; hence, the data werepooled and averaged thereof. Data wereanalyzed following analysis of variance usingStatistix 8.1 (Analytical Software, Tallahassee,FL, USA) software. The differences betweentreatments were separated using the LeastSignificance Difference (LSD) test at 0.05%probability level. Graphical presentation andregression analysis were made using Sigmaplot (Systat Software Inc., San Jose, CA, USA).

RESULTS

Experiment-I: Influence of aqueousextracts of parthenium on the germinationof wheat and canola in Petri plates

Pronounced variations in germinationattributes of wheat and canola were observedunder the influence of parthenium extractfractions and aqueous extract concentration(Figure 1). Higher concentrations (7.5% and10%) of all the extract fractions delayed timeto start germination (TSG) of both test speciesup to one and a half day but such a delaywas insignificant at a lower extract (2.5%)concentration (Figure 1). Whole plant, leaf androot extracts of parthenium had a significantbearing on T50 in canola, while T50 of wheatwas affected only by extract concentration(Table 2). Maximum delay in T50 was observedat the highest extract concentration (10%).Interactive effect of extract fractions withconcentration was also significant (p≤0.05) forMGT. Significant interaction implied that atlower concentrations (2.5-5%), leaf extract wasmore suppressive than whole plant and rootextract. Nevertheless, MGT of wheat did notvary significantly between whole plant and leafaqueous extract of parthenium. For canola,significantly higher MGT was noticed for wholeplant aqueous extract at all concentrationsthan that realized for leaf and root extracts(Figure 1). Nevertheless, significantly lower GIwas recorded for whole plant and leaf aqueousextracts that were statistically similar. In thecase of canola, GI was significantly affectedby the aqueous extract concentration only(Table 2) and increasing extract concentrationdiminished GI of canola to a greater extent.Regarding FGP, an interactive effect wassignificant for both wheat and canola.

Leaf extract was more suppressive inwheat than whole plant and root extract atall concentrations. However, differencesbetween whole plant and root extract werenonsignificant at a lower concentration (2.5%).At a higher concentration, least suppressionof FGP was observed for root extract (10%).Different parthenium extract fractions at alower concentration (2.5%) had no significanteffect on FGP of canola as compared withcontrol. However, with any increase in furtherextract concentration, FGP was reduced toa greater extent by whole plant extracts,although at higher (10%) concentrations adifference among whole plant, leaf, and rootextracts for FGP was nonsignificant (Figure 1).Final germination was inhibited only whenextract concentration exceeded 2.5% and wasreduced by 44% (whole plant), 51% (leaf) and22% (root) with parthenium extracts applied at10% concentrations. Such a reduction in thegermination of canola was 51%, 48% and 52%,respectively for above extract fractions. Higherextract concentrations (7.5 and 10%) also ledto mortality of germinated seedlings while atlower concentrations (2.5 and 5%) seedlingswere malformed and distorted.

Experiment-II: Influence of soil appliedaqueous extracts of parthenium onemergence and seedling growth attributesof wheat and canola

Soil applied extract fractions of partheniumand their concentrations did not significantlyinfluence TSE in both test species (Table 2).In wheat, E50 was significantly affected bydifferent extract fractions and concentrations.However in canola, only extract concentrationshad significant effect on E50. Maximumdelay in E50 was observed at highest extractconcentration (10%) in both species (Figure 2).Regarding MET, all the parthenium extractfractions were statistically similar with eachother for wheat. Nevertheless, a significant(p≤0.05) interaction between extract fractionsand concentrations was noticed for METof canola (Table 2). Significant interactionsuggested that for any particular concentrationwhole plant extract had higher MET than leafextract or root extract. In both test species, EIwas significantly affected by partheniumextract fractions and different concentrations;

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LSDLSD

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LSD is shown for the interaction between different plant fractions and aqueous extract concentrations.

Figure 1 - Influence of different plant fractions and aqueous extract concentrations of parthenium on different germination attributesof wheat and canola in Petri plates experiment.

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however, interaction between these two factorswas nonsignificant (Table 2). Increasing extractconcentration showed lower values of EI ascompared with control (Figure 2). Extractconcentrations of 2.5-7.5% showed statisticallysimilar EI in wheat that declined furtheras the extract concentration was raisedto 10% (Figure 2). Application of aqueousparthenium extract showed a slight yetsignificant reduction in FEP of wheat onlywhen the extract concentration exceeded5%. A significant two-way interactionbetween parthenium fractions and extractconcentration was observed regarding FEP ofwheat and canola. A significant interaction(p≤0.05) indicated that at low concentration(2.5%), whole plant and leaf extract were notsignificantly different from each other(Figure 2). Whole plant and leaf extract alsoshowed a statistically similar FEP suppressionwhen applied at a higher concentration(10%), yet such suppression was considerablyhigher than that realized for root extract ofparthenium, particularly in canola (Figure 2).

A differential suppression of seedlinggrowth of the test species was observed underthe influence of different extract fractions ofparthenium and their concentrations. Shootlength of wheat was significantly affected

by parthenium extract fractions and theirconcentrations while shoot length of canola wasonly affected by the extract concentration(Table 2; Figure 3). Among extract fractionssignificantly (p≤0.05) less shoot length of wheatwas recorded for whole plant extract. Allthe extract concentrations reduced shootlength of wheat as compared with controland 10% concentration was more suppressiveto shoot length in both species (Figure 3). Rootlength of both test species was decreasedwith increase in extract concentration. Alower extract concentration (2.5%) did notsignificantly reduce root length of both testspecies over control. However, further increaseshowed a significant suppression of root lengthas compared with control (Figure 3). Reductionin shoot and root length was reflected in theform of a reduced seedling biomass. Increasein extract concentration was concomitantwith decrease in seedling dry biomass ofboth test species. Leaf and whole plant extractswere more suppressive than root extracteven at lower (2.5%) concentration (Figure 3).An interactive effect between extract fractionsand concentration was significant (p≤0.05)regarding seedling dry biomass of canola.Seedling dry biomass of canola did not varysignificantly (p≤0.05) among extract fractionsat 10% concentration (Figure 3).

Table 2 - Summary of analyses of variance (ANOVA) for the influence of different plant fractions and aqueous extract concentrationsof parthenium, and their interactions on germination/emergence, seedling growth, and biochemical attributes of wheat and canolain petri plates and soil-filled thermocol trays experiments

Petri plates experiment Soil-filled thermocol trays experiment. Source of Variation

TSG T50 MGT GI FGP TSE E50 MET EI FEP SL RL TDB Chl. contents Phenolics

Wheat

Concentration (Conc.) ** ** ** ** ** * * ** ** ** ** ** ** ** **

Extract fraction (Ext.) * ns ** ** ** ns * ns ** ns ** ** ** ** **

Conc. × Ext. ns ns * * * ns ns ns ns * ns ns ns * *

CV 11.65 10.53 6.82 11.47 5.98 16.06 9.49 7.67 5.22 3.95 6.59 9.14 13.82 15.22 14.52

Canola Concentration (Conc.) ** ** ** ** ** ns * ** ** ** ** ** ** ** ** Extract fraction (Ext.) ns * ** ns ** ns ns ** ** ** ns ns ** ** **

Conc. × Ext. ns ns * ns ** ns ns * ns * ns ns ** ns ns

CV 14.73 11.89 5.51 14.30 6.58 15.46 14.35 8.42 7.42 4.95 11.55 16.02 9.56 14.83 13.56

** and * denote significance at the 0.01 and 0.05 probability levels, respectively. ns: nonsignificant, CV: Coefficient of variation, TSG:time to start germination, T50: time taken to 50% germination, MGT: mean germination time, GI: germination index, FGP: finalgermination percentage, TSE: time to start emergence, E50: time taken to 50% emergence, MET: mean emergence time, EI: emergenceindex, FEP: final emergence percentage, SL: shoot length, RL: root length, TDB: total seedling dry biomass, Chl: chlorophyll.

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Figure 2 - Influence of different plant fractions and aqueous extract concentrations of parthenium on emergence attributes of wheatand canola in soil-filled thermocol trays experiment.

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Leaf chlorophyll contents of wheat seedlingwere significantly affected by interactionbetween parthenium fractions and extractconcentration (Table 2). At a low extractconcentration (2.5%), root extract did notreduce chlorophyll contents in wheat whereaswhole plant and leaf extract showed a 32 and37% reduction (Figure 4). At higher extractconcentrations (7.5 and 10.0%), differentplant fractions resulted in a similar level ofsuppression in chlorophyll contents. Forcanola, main effects of parthenium fractionsand extraction concentrations weresignificant, while the interactive effect ofthese two factors was nonsignificant forchlorophyll contents. Leaf extract was more

suppressive than root extract. Moreover,increasing extract concentration diminishedchlorophyll significantly as compared withcontrol (Figure 4). Averaged across differentextract fractions, chlorophyll contents werereduced to the tune of 28 and 42% at an extractconcentration of 2.5 and 5.0%, respectively.Nonetheless, at higher concentrations (7.5and 10.0%), reduction magnitude correspondedto 64 and 68%, respectively, and bothconcentrations were statistically similar. Eachsuccessive increase in extract concentrationcaused significant (p≤0.05) increase inphenolic contents. Whole plant extract recordedmore phenolic contents at all concentrationsin wheat, while in canola, leaf extract shwoed

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gth

(cm

)

4.0

4.5

5.0

5.5

6.0

Shoo

t len

gth

(cm

)

4.8

5.4

6.0

6.6

7.2

Shoo

t len

gth

(cm

)

10

12

14

16

18

Whole plant (R2=0.87)Leaf (R2= 0.99) Root (R2=0.90)

Whole plant (R2=0.86)

Root (R2=0.99)Leaf (R2=0.98)


Root (R2=0.89)Leaf (R2=0.90)


Root (R2=0.99)Leaf (R2=0.98)


Root (R2=0.92)Leaf (R2=0.83)


Root (R2=0.85)Leaf (R2=0.66)

LSD LSD

LSDLSD

LSD LSD

Wheat Canola


Figure 3 - Influence of different plant fractions and aqueous extract concentrations of parthenium on seedling growth ofwheat and canola in soil filled thermocol trays experiment.

Concentration (%) Concentration (%)

Sho

ot le

ngth

(cm

)

Sho

ot le

ngth

(cm

)

Roo

t len

gth

(cm

)

Roo

t len

gth

(cm

)

See

dlin

g bi

omas

s (m

g se

edlin

g-1)

See

dlin

g bi

omas

s (m

g se

edlin

g-1)

KHALIQ, A. et al.


20

more phenolic contents at 7.5% and 10%concentrations (Figure 4). The interactionbetween parthenium fractions and extractconcentration regarding phenolic contents wasonly significant for wheat crop (Table 2).

DISCUSSION

The present study demonstrated thatthe aqueous extracts of parthenium wereinhibitory to the germination and seedlinggrowth of wheat and canola. Such aninhibitory activity of aqueous partheniumextracts may be due to the presence ofsuppressive allelochemicals in these extracts.Batish et al. (2002) have reported that extractsprepared from parthenium residues were richin allelochemicals (phenolics) and exhibitedphytotoxicity to the crops. Living as well asdead weed tissues of parthenium that are leftin the soil after the completion of the life cycle

can pose deleterious effects on subsequentcrops by the release of allelochemicals upondecaying (Batish et al., 2007; Khaliq et al.,2015). These allelochemicals are reported tobe present in almost all plant parts, includingstems, leaves, flowers, buds, pollen grains,seeds, fruits, roots and rhizomes (Singh et al.,2003). However, differences are observedamong species regarding their allelopathicpotential and in their abilities to producetoxins in various parts (Qasem & Foy, 2001;Tanveer et al., 2010), and parthenium is noexception (Khan et al., 2012). Different typesof allelopathic compounds have been reportedto be released from parthenium leaves(Swaminathan et al., 1990), stems (Mersie andSingh, 1988) and roots (Almodóvar-Vegat et al.,1988). Sesquiterpene, lactones and phenolicshave been implicated for allelopathicactivities of parthenium and such compoundsare water soluble (Picman & Picman, 1984;

0.0 2.5 5.0 7.5 10.0

Tota

l sol

uble

phe

nolic

(mg

g-1 F

W)

45

60

75

90

105

Tota

l Chl

orop

hyll

(mg

g-1 FW

)

0.6

1.2

1.8

2.4

0.0 2.5 5.0 7.5 10.0

Tota

l sol

uble

phe

nolic

(mg

g-1

FW)

15

30

45

60

75

Tota

l Chl

orop

hyll

(mg

g-1 F

W)

0.7

1.4

2.1

2.8

LSD

Wheat Canola

LSD

LSD LSD

Leaf (R2= 0.96) Whole plant (R2= 0.92)

Root (R2= 0.99)

Leaf (R2= 0.90) Whole plant (R2= 0.94)

Root (R2= 0.89) Leaf (R2= 0.89) Whole plant (R2= 0.75)

Root (R2= 0.97)



Figure 4 - Influence of different plant fractions and aqueous extract concentrations of parthenium on total chlorophyll andsoluble phenolic contents of wheat and canola in soil filled thermocol trays experiment.

Concentration (%)

Tota

l chl

orop

hyll

(mg

g-1 F

W)

Concentration (%)

Tota

l chl

orop

hyll

(mg

g-1 F

W)

Tota

l sol

uble

phe

nolic

(mg

g-1 F

W)

Tota

l sol

uble

phe

nolic

(mg

g-1 F

W)



Swaminathan et al., 1990). Difference in theactivity of aqueous parthenium extractsprepared from different fractions in suppressinggermination of test species can be attributedto quantitative and qualitative differences inallelochemicals present in these extracts.Alterations in germination of the test speciesupon exposure to allelochemicals have beenexplained as a secondary expression of inducedphysiological and biochemical changes in cellultra-structures, membrane integrity andpermeability, de novo synthesis of certaincompounds and enzymatic activity duringgermination (Weir et al., 2004; Gniazdowska& Bogatek, 2005). Rajendiran (2005) hasreported a number of chromosomal aberrationsin dividing cells under the influence ofparthenium extract which increasedsignificantly with increasing concentrationsand durations of exposure.

Seedling growth of wheat and canola wasadversely effected by various extract fractionsof parthenium at different concentrations.Canola was more sensitive as compared towheat crop. Maharjan et al. (2007) havereported that inhibition in seed germinationof the crucifer species (Raphanus sativus,Brassica campestris and B. oleracea) was morepronounced as compared to Oryza sativa,Triticum aestivum, Ageratina adenophora andArtemisia dubia even at a low concentration.It was noted that species varied considerablyin their sensitivity to aqueous extracts ofparthenium (Belz et al., 2007; Rashid et al.,2008). Differential allopathic suppressionin test species in the present study is alsoin line with the findings by Khaliq et al.(2015).

Soil application of aqueous extracts ofdifferent parthenium fractions reduced theleaf chlorophyll content in both test species(Figure 4). Decrease in chlorophyll contentmay be due to exposure of growing seedlingsto phytotoxic compounds which are mostlyphenolic in nature. Phenolic compounds arereported to decrease leaf expansion, chlorophyllcontent, photosynthesis and electron transport(Colpas et al., 2003; Norman et al., 2004).Phytochemical-mediated reduction inseedling photosynthetic pigments primarilydue to phenolic acids has also been reportedby Khaliq et al. (2012). Our results have

revealed that whole plant and leaf extracts weremore suppressive than root extract to both testspecies at all concentrations. It may be due tothe presence of more phenolic contents in leafthan whole plant and root extracts (Table 1).Phytotoxicity of foliar parts of partheniumweed is well documented (Belz et al., 2007; Li& Jin, 2010). Xuan et al. (2004) have reportedthat foliar parts have more phytotoxicitybecause of greater biomass and metabolicactivities. Tefera (2002) has reported that thegermination of Eragrostis was more suppressedby the application of parthenium leaves andflower extracts as compared to stem androot extracts. Belz et al. (2007) showed thatparthenin isolated and purified from theaqueous extract of parthenium leaves underlaboratory conditions was significantlyphytotoxic, and reduced the germination andseedling growth of wheat.

Some authors have reported that theinhibitory effects of aqueous extractsoriginated from changes in pH and osmoticpotential and hence the raising concern aboutallelopathy and its ecological existence andrelevance (Conway et al., 2002; Sisodia, 2008).In the present study, pH of extract fractions(whole plant, leaf and root) ranged from 6.6 to7.8 (Table 1) and osmotic potential rangedfrom 0.04 to 0.20 -Mpa, which are unlikely tocause an inhibitory effect on plant growth(Mersie & Singh, 1987). Any growth reductionwas presumably due to inhibitors. The amountof phenolics was also quantified in extractsfrom different fractions of parthenium andwas in the order of leaves>whole plant>rootextracts (Table 1). A 10% leaf extractconcentration showed about 1345 μg mL-1 ofsoluble phenolics.

Parthenium extracts suppressed thegermination of test species to a greater extentwhen evaluated in Petri plates using filterpaper as a substratum than when soil was usedas a growth medium. Slope of lines indicatinga drop in germination with increased extractconcentration was steeper in Petri plates fordifferent parthenium plant fractions (Figure1)as compared to the pot experiment (Figure 2).Even mortality of seedlings was observedin Petri plates but none in soil-filled pots.In the soil, allelopathic compounds aresubjected to various transformations such

KHALIQ, A. et al.


22

as the utilization by soil microorganisms(Blum et al., 1999), chemical transformation(Okumura et al., 1999) and polymerization(Wang et al., 1986) among others actingeither simultaneously or sequentially. Thesemodify persistence, concentration, availabilityand biological activities of allelochemicals.Allelochemicals are also known to affect thephysico-chemical soil properties and arequalitatively and quantitatively affectedby these factors (Inderjit et al., 1996).Moreover, soil also possesses the ability tometabolize or detoxify allelochemicals. Suchtransformations are unlikely to occur in thePetri plates.

Previously, numerous studies (Inderjit &Weston, 2000) have obtained contrastingresults under controlled and natural fieldconditions. It is almost impossible to simulateexact field conditions in a bioassay; howeverin the present study, soil was also used asa growing medium with the objectives ofmaintaining the physical, chemical, andbiological soil factors of the natural setting,as soil possesses the ability to detoxifyallelochemicals. The aqueous partheniumextract contained appreciable quantitiesof phenolic compounds (most of theallelochemicals responsible for biologicalactivity are phenolics in nature) but responsewas less as compared to that observed in Petridish. There is strong reason to believe thatcontrary to petri dish, pot experiments usingthe extraction methods and concentrationsare representative of what could happen in thefield.

The present study concludes that thebioassay conducted under a controlledcondition using filter paper as substratum canbe misleading due to the overestimation ofallelopathic response and potential of receiverand donor species. It implies that thresholdconcentrations of allelochemicals for testspecies in Petri plates are rarely reachedunder field conditions (soil) merely becausesuch compounds will not accumulate to levelsthat can cause a significant allelopathicresponse. Moreover, the results demonstratedthat leaf extracts of parthenium were mostphytotoxic, while canola was the mostsusceptible test species in both Petri platesand soil.

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11 a atividade fitotóxica de parthenium contra trigo e canola

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